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<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Set集合实践</title>
</head>

<body>
  <script>
    let arr = [1,2,3,4,5,4,3,2,1];
    // 1. 数组去重
    let result = [...new Set(arr)];
    console.log(result);

    // 2. 交集
    let arr2 = [4,5,6,5,6];
    /* let result2 = [...new Set(arr)].filter(item => {
      let s2 = new Set(arr2);
      if(s2.has(item)) {
        return true;
      } else {
        return false;
      }
    }) */

    let result2 = [...new Set(arr)].filter(item => new Set(arr2).has(item))
    console.log(result2)

    // 3. 并集
    let union = [...new Set([...arr, ...arr2])];
    console.log(union);

    // 4. 差集
    // let diff = [...new Set(arr)].filter(item => !new Set(arr2).has(item));
    let diff = [...new Set(arr2)].filter(item => !new Set(arr).has(item));
    console.log(diff);

  </script>
</body>

</html>